Analysis of data from the Walnut Creek Contraceptive Drug Study showed a significant increase in risk of venous thromboembolic disease in the absence of surgery, trauma, malignancy, pregnancy, and the puerperium for women with a previous history of thromboembolism, hypertension, diabetes, varicose veins, gallbladder disease, and cigarette smoking. Education, marital status, parity, use of noncontraceptive estrogens, and obesity were not associated with an increase in risk of the disease. When only cases of the disease in the absence of all known predisposing causes (idiopathic cases) were analyzed, both oral contraceptive use and smoking remained as independent risk factors; there was no evidence of a positive interaction between them.